Python Classroom notes 21/Jul/2026

Command line applications (CLI)

• These applications process the commands and arguments

# windows
ping google.com
# linux
ping -c 4 google.com

• Any command line application will generally have arguments
• Arguments are of two types
  • positional arguments: position matters
  • keyword arguments: this argument has a key and a value
    • short form -<char>: Examples are -a test -c 4
    • long form --<work>: Examples are --anchor test --count 4
• Arguments can be defined as
  • optional: where if the user does not pass a value we assume default
  • required: where the user has to pass and argument

Simple CLI Based Application in python

• Topic: Standard Library

• Lets build a cli application which takes two arguments and display the sum of two numbers, lets call this add

• in the world of python module refers to the python file and the name of module filename without extension

add.py  => add
add_test.py => add_test

• Reusable prompt

You are an expert in python.

I will be passing a standard libraries name

I want you to summarize the purpose of this standard library

Some examples of what we can do this standard library.

• Create a file called as add.py with the following code

"""
This module is a cli application which adds two numbers
"""

# import a standard module
import sys

print(sys.argv)

if __name__ == "__main__":
    number_1 = int(sys.argv[1])
    number_2 = int(sys.argv[2])
    result = number_1 + number_2
    print(f"result is: {result}")

• Now navigate to the terminal and execute the following python add.py 1 3

• CLI Applications generally need to validate the inputs i.e. arguments passed

• To simplify the cli application building we have two possible options

  • Standard library: We have argparse

  • Community Library:: We have click

• To summarize we need to

  • Process arguments
  • Validations
  • Help/Documentation for cli

• Exercise: Build a cli using argparse to convert kilos into pounds

python convert.py 13

`13 kilos => 28.6601 pounds`

Financial calculator

• Lets build a financial calculator which helps in

  • EMI calculators
  • Intrest Calculators

• The core idea is to learn and apply

  • python standard libraries
  • Object oriented concepts
  • Design patterns
  • Best Practices